This invention relates to signal processor systems providing a digital output for use in the correction of non-uniformities in the output of matrix arrays. It is particularly, but not necessarily exclusively, suitable for use with infra-red arrays.
In general, matrix arrays suffer from non-uniformity in output from the individual elements of the matrix array. This is caused by each element of the matrix array having for example, its own characteristic responsivity and leakage current, and is seen in the matrix array output as a pattern of offset values. These offset values may be 2000 times the random noise output of the array.
In order to obtain useful digital information from a matrix array, the offset values must be removed from the output. A method of doing this is to show the array a black body of a given uniform temperature; the output from the array can then be used to cancel the offset values obtained during subsequent use. A problem with this method, in addition to having to use a static reference source, is that the dynamic range of the system is directly related to the range of offset values obtained and the size of the digitiser. With existing large-size digitisers, the sampling rate is relatively slow, and where a higher sampling rate is necessary, a small-size digitiser must be provided. For example a sampling rate of 1 MHz can only be presently obtained by an 8-bit digitiser.
It is therefore an object of this invention to provide a signal processing system in which the dynamic range of the system is not significantly prejudiced by the use of a small-size digitiser.